fork join框架_Java 7：Fork / Join框架示例

fork join框架

Java 7中的Fork / Join Framework专为可分解为较小任务的工作而设计，并将这些任务的结果组合起来以产生最终结果。通常，使用Fork / Join Framework的类遵循以下简单算法：

// pseudocode
Result solve(Problem problem) {if (problem.size < SEQUENTIAL_THRESHOLD)return solveSequentially(problem);else {Result left, right;INVOKE-IN-PARALLEL {left = solve(extractLeftHalf(problem));right = solve(extractRightHalf(problem));}return combine(left, right);}
}

为了证明这一点，我创建了一个示例，使用fork / join从一个大型数组中查找最大数量：

import java.util.Random;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.RecursiveTask;public class MaximumFinder extends RecursiveTask<Integer> {private static final int SEQUENTIAL_THRESHOLD = 5;private final int[] data;private final int start;private final int end;public MaximumFinder(int[] data, int start, int end) {this.data = data;this.start = start;this.end = end;}public MaximumFinder(int[] data) {this(data, 0, data.length);}@Overrideprotected Integer compute() {final int length = end - start;if (length < SEQUENTIAL_THRESHOLD) {return computeDirectly();}final int split = length / 2;final MaximumFinder left = new MaximumFinder(data, start, start + split);left.fork();final MaximumFinder right = new MaximumFinder(data, start + split, end);return Math.max(right.compute(), left.join());}private Integer computeDirectly() {System.out.println(Thread.currentThread() + ' computing: ' + start+ ' to ' + end);int max = Integer.MIN_VALUE;for (int i = start; i < end; i++) {if (data[i] > max) {max = data[i];}}return max;}public static void main(String[] args) {// create a random data setfinal int[] data = new int[1000];final Random random = new Random();for (int i = 0; i < data.length; i++) {data[i] = random.nextInt(100);}// submit the task to the poolfinal ForkJoinPool pool = new ForkJoinPool(4);final MaximumFinder finder = new MaximumFinder(data);System.out.println(pool.invoke(finder));}
}

MaximumFinder类是一个RecursiveTask ，它负责从数组中查找最大数目。如果数组的大小小于阈值（5），则通过遍历数组直接找到最大值。否则，将数组分成两半，每半递归并等待它们完成（ join ）。一旦我们得到了每一半的结果，我们就可以找到两个的最大值并返回。

参考： Java 7：我们的JCG合作伙伴 Fahd Shariff在fahd.blog博客上提供的Fork / Join Framework Example 。